Reducing lift on different body shape cars

[aerohead]

Originally Posted by JulianEdgar

This is very important because, as you have indicated in this case, I have found that time and time again Aerohead misquotes references.

It's only when you go and check that you find that to be the case - the quotes sound quite authoritative...

If I've listed a specific reference, I'm providing either a verbatim quote, or have simplified the text for brevity. Page numbers are provided if one is interested in vetting.

[JulianEdgar]

Originally Posted by aerohead

I believe the context of that comment had to do with measuring pressures. Something you've yet to make a compelling case for.

Naaah, pressures don't matter at all in car aero. They're only responsible for 80-90 per cent of aerodynamic drag on cars.

Gee, why would we be interested in pressures?!

[aerohead]

Originally Posted by JulianEdgar

[jaw drops].

Now you're just off in fantasy land, I am afraid. Why not add the calories of what you had for lunch?

Seriously, this is just absolute rubbish.

It's just aerodynamic engineering to the rest of the world.

[aerohead]

Originally Posted by JulianEdgar

Naaah, pressures don't matter at all in car aero. They're only responsible for 80-90 per cent of aerodynamic drag on cars.

Gee, why would we be interested in pressures?!

I'm very interested at how your pressure readings will lead to a Cd 0.09 automobile.

[AeroMcAeroFace]

Originally Posted by aerohead

I'm very interested at how your pressure readings will lead to a Cd 0.09 automobile.

Isn't the point though, that we are starting with a 0.3-0.35 vehicle? There are huge gains to be made, even if there are vortices, downwash, and attached flow. I don't think there is anybody here realistically expecting to get to 0.09 without starting from scratch.

"1) so remove the constant-diameter cylindrical section.
2) join the nose and tail section to form the streamlined body of revolution.
3) use Hucho's drag table from Hoerner to ascertain the Cd of the streamlined body you've just created.
4) subtract out the skin friction no longer present from the elongated body.
5) bifurcate what's left, longitudinally, to create the half-body.
6) double the Cd of the streamlined body to get the drag of the half-body.
7) now add wheels, and wheel drag, as Jaray and Buchheim did, and tell me what you come up with."

what you come up with is something that has no relevance to anyone here. If we were going for 0.09, why wouldn't we use CFD to guide the shape, much like they do for solar cars.

This is a disconnect, between aerohead and most people on ecomodder. Instead of starting with a normal car with pressure drag and hoping to make a 20% difference, aerohead believes that we are all here starting out with the creme egg van and looking to go to extreme low levels of drag.

[aerohead]

Originally Posted by AeroMcAeroFace

Isn't the point though, that we are starting with a 0.3-0.35 vehicle? There are huge gains to be made, even if there are vortices, downwash, and attached flow. I don't think there is anybody here realistically expecting to get to 0.09 without starting from scratch.

"1) so remove the constant-diameter cylindrical section.
2) join the nose and tail section to form the streamlined body of revolution.
3) use Hucho's drag table from Hoerner to ascertain the Cd of the streamlined body you've just created.
4) subtract out the skin friction no longer present from the elongated body.
5) bifurcate what's left, longitudinally, to create the half-body.
6) double the Cd of the streamlined body to get the drag of the half-body.
7) now add wheels, and wheel drag, as Jaray and Buchheim did, and tell me what you come up with."

what you come up with is something that has no relevance to anyone here. If we were going for 0.09, why wouldn't we use CFD to guide the shape, much like they do for solar cars.

This is a disconnect, between aerohead and most people on ecomodder. Instead of starting with a normal car with pressure drag and hoping to make a 20% difference, aerohead believes that we are all here starting out with the creme egg van and looking to go to extreme low levels of drag.

If you can afford Dassault's Exa POWERFLOW go for it. I considered that EcoModder members might pool funds together to obtain use of it. A number of calls went un-returned. They wouldn't tell me what hardware was necessary to run it, nor what leasing the software, or using their online resources would cost. I gave up.
Which left only the dimensional analysis.
Some of the solar cars winning the World Solar Challenge are already using the template. The lowest drag 'car' ever measured uses it. It was relevant to them. What do I make of your comment?
The 'template' works in their wind tunnels and CFD, but not at EcoModder?

[JulianEdgar]

Originally Posted by aerohead

If you can afford Dassault's Exa POWERFLOW go for it. I considered that EcoModder members might pool funds together to obtain use of it. A number of calls went un-returned. They wouldn't tell me what hardware was necessary to run it, nor what leasing the software, or using their online resources would cost. I gave up.
Which left only the dimensional analysis.
Some of the solar cars winning the World Solar Challenge are already using the template. The lowest drag 'car' ever measured uses it. It was relevant to them. What do I make of your comment?
The 'template' works in their wind tunnels and CFD, but not at EcoModder?

This forum is called Ecomodder.

Modifications to cars. So we're interested in what will achieve good results on our cars.

Now that the template has been proved to be largely invalid in doing that, you move the goalposts to now this site being about developing ultra-low drag cars from scratch. If we were in fact doing that, I think all five(!) low drag shapes that have been published in the literature would make good starting points.

But as far as I know, that's not what we're doing here.

[JulianEdgar]

Originally Posted by aerohead

If you can afford Dassault's Exa POWERFLOW go for it. I considered that EcoModder members might pool funds together to obtain use of it. A number of calls went un-returned. They wouldn't tell me what hardware was necessary to run it, nor what leasing the software, or using their online resources would cost. I gave up.
Which left only the dimensional analysis.
Some of the solar cars winning the World Solar Challenge are already using the template. The lowest drag 'car' ever measured uses it. It was relevant to them. What do I make of your comment?
The 'template' works in their wind tunnels and CFD, but not at EcoModder?

Er, no. It left aerodynamic testing and development, not guesswork from drawings.

[aerohead]

Originally Posted by JulianEdgar

This forum is called Ecomodder.

Modifications to cars. So we're interested in what will achieve good results on our cars.

Now that the template has been proved to be largely invalid in doing that, you move the goalposts to now this site being about developing ultra-low drag cars from scratch. If we were in fact doing that, I think all five(!) low drag shapes that have been published in the literature would make good starting points.

But as far as I know, that's not what we're doing here.

Correct me if I'm mistaken, however, all I've seen so far, are uncorroborated statements, with no empirical, laboratory evidence. And quite the contrary.
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As to the Volkswagen 'templates', let's discuss those:
* The VW-Blunt Body ( solid-border rendering ) is a 'Go!. It is the AST-II form. And at Cd 0.15, it has the potential for lower drag with elongation, perhaps Cd 0.14.So thanks for the it's recommendation!
* The VW-Blunt Body ( dashed-line bordered rendering ) is the 1922, Wolfgang Klemperer, 'minivan' basic body. And a great mystery shape, as it's Cd doesn't change between 1922 and 1981. If you could see out of it, it would be a miracle! Perhaps in the future, with synthetic vision, as IHPV land speed record bicycle are using, it wouldn't be an issue. So I excluded it as a candidate for us here at EcoModder.
* The VW-Drop Shape is also a fail with respect to forwards outward visibility. Reason I don't endorse its use. It's also already 100% boat-tailed, with zero-opportunity for lower drag beyond Cd 0.16.
* The VW-Flow-Body is a 'Go', as it's essentially a 'template' form, with 23-degrees instead of 22.5-degrees rear slope maximum. And with Cd 0.15 as a truncated form, and Cd 0.14 as a 'long-tail, it's a perfect candidate for the extensible boat-tail. It also has the facility for perfect forwards outward vision. Thanks again for the thumbs-up!
* The AVA Streamline Shape, is, of course, the 1938 Schl'o'rwagen, by Ludwig Prandtl. Cd 0.186. It has perfect forwards outward vision. It is, unfortunately, already Verjungungsverhaltnis- limited, at Cd 0.186, so there's no potential for lower drag. Why I cannot endorse it either.

[aerohead]

Originally Posted by JulianEdgar

Er, no. It left aerodynamic testing and development, not guesswork from drawings.

At $ 4,000 / hour, are you prepared to underwrite all member costs? I believe we have, on the order of over 30,000 members.
Very generous of you!